1. Field of the Invention
The present invention relates to an image forming apparatus provided with an image bearing member on the outer surface of which a toner image is to be formed, and an image forming unit employed in this image forming apparatus.
2. Description of the Related Art
There has been known an image forming apparatus constructed such that an electrostatic latent image is formed on the circumferential surface of a photoconductive drum (image bearing member) by reading a document image or based on image information transmitted from an external computer or the like, toner is supplied toward this electrostatic latent image from a developing device to form a toner image on the circumferential surface, and this toner image is transferred to a sheet.
In such an image forming apparatus, a proper image forming process is hindered in some cases due to residual toner remaining on the circumferential surface of the photoconductive drum after an image transferring process to a sheet and/or the deposition of nitrogen oxides produced during a high voltage charging process performed before an electrostatic latent image is formed on the circumferential surface.
In order to solve such problems, Japanese Unexamined Patent Publication No. 2006-259274 discloses an image forming apparatus provided with a coating bar made of a solid lubricant such as zinc stearate, wherein the lubricant from this coating bar is supplied to the circumferential surface of a photoconductive drum. In this apparatus, a fur brush driven to rotate is interposed between the coating bar and the photoconductive drum and the lubricant from the coating bar is applied to the circumferential surface of the image bearing member via this fur brush. Since frictional resistance of the circumferential surface of the photoconductive drum is reduced to make this circumferential surface lubricant by the application of the lubricant to the circumferential surface of the photoconductive drum, the deposition of foreign matters such as residual toner and nitrogen oxides is suppressed and an image failure caused by these extraneous matters is effectively prevented.
However, in the conventional image forming apparatus, the lubricant is mainly applied to an image formation region on the circumferential surface of the photoconductive drum. Thus, the deposition of foreign matters is prevented from this image formation region, but no consideration is made for the opposite end portions of the photoconductive drum not belonging to the image formation region.
In order to define tiny clearances (gaps) between the circumferential surface of a developing roller of a developing device and that of the photoconductive drum, gap rollers are in contact with the opposite end portions of the photoconductive drum in some cases. Thus, if extraneous matters are accumulated on the surfaces of the opposite end portions of the photoconductive drum, the gap rollers run onto and run off from these extraneous matters according to the rotation of the photoconductive drum, thereby varying a gap size. This makes toner supply to the circumferential surface of the photoconductive drum from the developing roller unstable, thereby presenting a problem of being unable to form a stable toner image on the circumferential surface of the photoconductive drum.